In this project I am going to investigate rates of reaction of an indigestion tablet when added to hydrochloric acid. The variable I am going to use will be the temperature of the acid. (All background knowledge used in this project was taken from previous experience – notes and experiments from work done in year nine) What are rates of reaction? The rate of a reaction is the speed at which a reactant is turned into the product. Chemical reactions can take place at very different rates (eg. explosions, rock formations). A rate is measured as:
A change in something (eg.loss of mass/mass of gas given off) Divided by The time it takes to change/disappear Rates of reactions can be measured in two different ways: How fast reactants disappear How fast products appear Many factors affect rates of reaction: Surface area The greater the surface area of a solid, the greater the area of the particles that is exposed and likely to collide with other particles, meaning more successful collisions can take place per second. Therefore reaction between acid and a finely powdered salt will take place faster than a reaction between the same acid and a lump of salt.
Concentration of solutions The rate of a reaction increases as the concentration of the solution increases. This is because there are more solute particles to collide with a fixed volume of solvent particles. Therefore more successful collisions take place. The rate of a reaction is directly proportional to its concentration (i. e. as concentration doubles, rate doubles. ) (This is assuming that any reactions taking place are not exothermic and that no other variables are changed) Temperature The rate of reaction increases as the temperature increases.
This is because at a higher temperature the particles move around faster (due to heat energy being converted into kinetic energy) and have more chance of colliding with each other. Also, there is a greater chance of effective collisions. However, unlike concentration, this is not proportional. As the temperature begins to increase, the rate increases slowly, but as it gets higher the rate increases faster, creating a curved graph. Catalysts Catalysts are substances which increase the rates of chemical reactions but are not used up or altered in any way altered themselves.
They provide an alternative method of collision requiring less energy. (eg. enzymes in the body are natural catalysts). Pressure of Gases When the pressure of a gas is increased, the molecules have less space to move around in. This increase in concentration makes them collide more often. What is ‘Collision Theory’? Collision theory states that the more successful collisions per second there are, the higher the rate of reaction. In order for a collision to be successful (or effective) there needs to be enough energy, speed and strength to break the bonds in the colliding molecules.
Collisions between molecules are stronger at higher temperatures. In an ineffective reaction, the molecules just rebound off each other. My Experiment I am going to investigate the relationship between rates of reaction and temperature. I chose temperature because it is easy to keep the concentration constant and from previous experiments I have noticed the graph has more points of interest than that of concentration (see page 2). I could do this in two different ways: Measure how fast reactants disappear
This can be measured either by weighing a solution before and after to check mass change, or by sight (for example seeing how long it takes before a cross under a cloudy solution is no longer visible. ) The latter is inaccurate and not easily measurable as human error plays too large a part. However, I could weigh the mixture before and afterwards Measure how fast products appear This can be measured in many different ways, depending on the state of the product. If it is a gas, the gas can be collected and measured in a gas syringe.
First, I need to look at the equations for the reactions of the active ingredients in the tablets with the acid. These active ingredients are: Magnesium Carbonate Calcium Carbonate Sodium Hydrogen Carbonate General Equation: Metal Carbonate + Acid –> Metal Salt + Carbon Dioxide + Water Magnesium Carbonate + Hydrochloric Acid –> Magnesium Chloride + Carbon These equations show that the final products are a metal salt, water and carbon dioxide. I can either measure the mass before and after adding the tablet to the hydrochloric acid or collect the gas given off.
I chose to measure the gas (after my preliminary experiments – see page 7) because: I think this method can be modified to produce good results. Also in the preliminary experiments I worked out a good volume of gas to collect (see page 7). It does rely on human judgement (in starting and stopping the stopclock) but all other methods involving timing do also.
Within this, there are two different ways that the gas given off can be measured: I can measure how long it takes for the reaction to give off a fixed volume of gas. I can see how much gas is given off in a certain time. I am going to use the first method, as I think that the stopclock will be more accurate than the gas syringe as I only want to measure the time to the nearest second. Also the gas syringe only has markings every for every 5cmi?? of gas given off, and therefore it would be easier to measure to a marking on the syringe. Prediction and Hypothesis.
I predict that as the temperature increases, the rate of reaction will increase also. This is because at a higher temperature there is more heat energy to be converted into kinetic energy, making the particles move around faster. Faster moving particles have more chance of colliding with each other and the greater quantity of heat and energy means more effective collisions are created. As I wrote earlier (see page 2), a graph of temperature/rate should look like this: a. Because the two wouldn’t mix at 0i?? C or less I have to start at a temperature above that. Therefore the graph won’t go through the origin.
b. To begin with the rate of reaction rises slowly. c. It increases faster as the temperature increases, giving a line which gets rapidly steeper. Plan NB. Although this is the final plan for the actual experiments, a lot of the volumes and other measurements weren’t worked out until the preliminary experiments were done (see pages 6, 7 and 8). In the preliminary experiment section I have specified the areas that I was investigating. Get out equipment as specified. Measure out 50cmi?? of hydrochloric acid (concentration 4mol/dmi?? ) into a conical flask using a burette.
Measure the temperature of the solution and adjust it until it is the required temperature (by adding more cold/hot water into the beaker it’s in). Make sure the gas syringe is back to 0. Add two whole tablets to the solution, put the bung in and start the stopclock (or get someone else to start the stopclock). Swirl the solution gently to aid the reaction. When 50cm i?? of gas has been collected stop the stopclock Remove the bung from the conical flask to avoid too much gas being collected. Note the temperature and the time taken. Repeat the experiment, and then do the same for six other temperatures.
To ensure that this is a fair test, there should only be one variable, temperature. Therefore the temperature of the acid is the only thing that I should change. I should try to keep the volume of acid the same (by using a burette), keep the concentration of acid the same, only use whole tablets (to keep the surface area the same) and try to swirl the acid in the same way each time. Range and Readings Before the preliminary experiments I had decided to take six readings, all with repeats. These readings would have been either five or 10i?? C apart and would have ranged from approximately 10i?? C to 50i?? C.
During the preliminary experiments I investigated this further (see page 8), and revised this original method. However, I did realise beforehand that there were several different ways I could get temperatures of 50i?? C. I could use a Bunsen burner to heat the acid or I could stand the acid in a beaker full of boiling or hot water. The second method seemed the best because it was easily controllable, the temperature wouldn’t rise too quickly, and you could also stand the acid in ice to cool it to 10i?? C. I didn’t change this part of the method, as it seemed to work effectively. Equipment Use Conical flask.
This will hold the hydrochloric acid and the tablets. It needs to have a bung in it and a tube with a bend in it which can be connected to the gas syringe, to stop any gas escaping during the reaction. As I am using two whole tablets, I don’t need to have one with a particularly wide neck. Clamp and clamp stand These will hold the gas syringe at the correct height to connect to the conical flask. Gas syringe This will measure the volume of gas given off during the reaction, or the length of time it takes to give off a given volume of gas (50cmi?? ). It should measure to the nearest cmi??.
Burette This will be used to measure out 50cmi?of hydrochloric acid accurately (it measures to half a cmi?? , and therefore is more accurate than for example a measuring cylinder. ) Thermometer This will be used to ensure the temperature is kept correct and constant leading up to the experiment. It measures to half a degree. Tub I will stand the conical flask in a tub full of hot water/ice which will bring the acid to the temperature needed. Stopclock This will time how long it takes to collect 50cmi?? of gas. This should be accurate to the nearest second. Diagram of Equipment Safety Certain safety precautions must be taken when using acids and other potentially harmful substances:
Goggles must be worn to protect eyes. This is especially important as I am heating acid (although gently) and hot acid may spit before or during the reaction. f there are spills with corrosive acids they must be cleaned up immediately and thoroughly to prevent accidents (for example slipping on acid), and any skin that comes into contact with the acid must be thoroughly washed. Hands should be washed anyway after using acid. After my experiment I must make sure that everything is cleared away effectively. I must not leave any acid or other substances out to prevent it becoming a safety hazard.